U.S. patent application number 10/476274 was filed with the patent office on 2004-09-23 for opaque film made of polylactic acids.
Invention is credited to Busch, Detlef D., Hade, Petra, Kochem, Karl-Heinz, Rosenbaum, Manfred, Rosenbaum, Marlies, Rosenbaum, Sonja.
Application Number | 20040185282 10/476274 |
Document ID | / |
Family ID | 7683261 |
Filed Date | 2004-09-23 |
United States Patent
Application |
20040185282 |
Kind Code |
A1 |
Rosenbaum, Sonja ; et
al. |
September 23, 2004 |
OPAQUE FILM MADE OF POLYLACTIC ACIDS
Abstract
The invention relates to an opaque biaxially oriented film made
of at least one layer that contains COC. This layer contains a
cycloolefin copolymer (COC) in a concentration of 0.5 to 30 wt %
with regard to this layer and contains a polymer made from
aliphatic hydroxycarboxylic acid units.
Inventors: |
Rosenbaum, Sonja; (Bous,
DE) ; Rosenbaum, Marlies; (Bous, DE) ;
Rosenbaum, Manfred; (Bous, DE) ; Hade, Petra;
(Saarbrucken, DE) ; Busch, Detlef D.; (Saarlouis,
DE) ; Kochem, Karl-Heinz; (Neunkirchen, DE) |
Correspondence
Address: |
CONNOLLY BOVE LODGE & HUTZ, LLP
P O BOX 2207
WILMINGTON
DE
19899
US
|
Family ID: |
7683261 |
Appl. No.: |
10/476274 |
Filed: |
March 29, 2004 |
PCT Filed: |
April 19, 2002 |
PCT NO: |
PCT/EP02/04324 |
Current U.S.
Class: |
428/480 ;
428/331; 428/500 |
Current CPC
Class: |
C08L 67/04 20130101;
Y10T 428/31692 20150401; C08L 67/04 20130101; Y10T 428/249953
20150401; C08J 2367/04 20130101; C08L 2666/16 20130101; Y10T
428/31786 20150401; C08J 5/18 20130101; Y10T 428/31681 20150401;
Y10T 428/31855 20150401; Y10S 428/91 20130101; Y10T 428/259
20150115 |
Class at
Publication: |
428/480 ;
428/500; 428/331 |
International
Class: |
B32B 027/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 30, 2001 |
DE |
101 21 150.3 |
Claims
1. Opaque biaxially oriented film comprising at least one
COC-containing layer, characterized in that this layer comprises at
least one polymer I made from at least one hydroxycarboxylic acid
and from 0.5 to 30% by weight, based on the layer, of a cycloolefin
copolymer (COC) having a glass transition temperature in the range
from 70 to 270.degree. C.
2. Film according to claim 1, characterized in that the cycloolefin
copolymer (CO C) is polynorbornene,
polydimethyloctahydronaphthalene, polycyclopentene or
poly(5-methyl)norbornene.
3. Film according to claim 1 or 2, characterized in that the
cycloolefin copolymer (COC) has a glass transition temperature in
the range from 80 to 200.degree. C.
4. Film according to one or more of claims 1 to 3, characterized in
that the polymer I is built up from at least one hydroxycarboxylic
acid comprising aliphatic hydroxycarboxylic acid units, preferably
comprising lactic acid units.
5. Film according to one or more of claims 1 to 4, characterized in
that the polymer I comprising aliphatic hydroxycarboxylic acid
units, preferably comprising lactic acid units, has a melting point
of 110-170.degree. C. and a melt flow index of 1-50 g/10 min.
6. Film according to one or more of claims 1 to 5, characterized in
that the COC-containing layer comprises from 1 to 25% by weight of
pigments, preferably TiO.sub.2, in each case based on the weight of
the layer.
7. Film according to one or more of claims 1 to 6, characterized in
that the COC-containing layer forms the base layer of the film, and
in addition a top layer built up from at least one polymer I made
from at least one hydroxycarboxylic acid is applied to one or both
sides of this base layer.
8. Film according to claim 7, characterized in that an interlayer
is arranged on one or both sides between the COC-containing base
layer and the top layer(s).
9. Film according to one or more of claims 1 to 8, characterized in
that the film is single-layer and consists of the CO C-containing
layer.
10. Film according to one of claims 1 to 9, characterized in that
the COC-containing layer forms a top layer or an interlayer of the
film.
11. Film according to one or more of claims 1 to 10, characterized
in that the film has COC-containing interlayers on both sides.
12. Film according to one or more of claims 1 to 11, characterized
in that the film has a density of less than 1.25 g/cm3, preferably
from 0.6 to 1 g/cm3.
13. Film according to one or more of claims 1 to 11, characterized
in that the COC-containing layer forms a top layer of the film, and
the outer surface of this layer is metallized.
14. Use of a film according to one of claims 1 to 13 as packaging
film, as twist-wrap film or as label film.
15. Process for the production of a film according to one or more
of claims 1 to 12, characterized in that a melt of PLA and COC is
extruded, where this melt temperature is at least 10.degree. C.
above the Tg of the COC, and the melt cools to form a pre-film, the
cooled pre-film is stretched in the machine direction at a
temperature of from 50 to 70.degree. C., and the longitudinal
stretching factor is in the range from 4 to 6.
16. Process according to claim 13, characterized in that the film
is stretched transversely at a temperature of from 70 to
100.degree. C. after the longitudinal stretching, and the
transverse stretching factor is in the range from 5 to 8.
Description
[0001] The present invention relates to an opaque, biaxially
oriented PHC film which includes at least one layer comprising
polymers based on hydroxy-carboxylic acids and a cycloolefin
copolymer (COC). The invention furthermore relates to a process for
the production of the PHC film and to the use thereof.
[0002] Opaque biaxially oriented films are known in the prior art.
These films are distinguished by a glossy, mother-of-pearl-like
appearance, which is desired for certain applications. In addition,
films of this type have a reduced density, which enables the user
to achieve increased yield.
[0003] The object of the present invention was to provide
environmentally friendly packaging which firstly can be produced
from renewable raw materials and secondly can be disposed of in an
environmentally friendly manner. In addition, the film should have
an opaque appearance and have a density of below 1.25
g/cm.sup.3.
[0004] The object is achieved by an opaque, biaxially oriented film
having at least one layer whose characterizing features consist in
that this layer comprises at least one polymer I made from at least
one hydroxycarboxylic acid (PHC) and from 0.5 to 30% by weight,
based on the layer, of a cycloolefin copolymer (COC) having a glass
transition temperature in the range from 70 to 270.degree. C.
[0005] For the purposes of the present invention, the term opaque,
biaxially oriented PHC film is taken to mean a film which has a
whiteness of at least 10%, preferably greater than 20%, and an
opacity of greater than 20%, preferably greater than 25%. In
general, the light transmission in accordance with ASTM-D 1003-77
of opaque films of this type is less than 95%, preferably less than
75%.
[0006] In order to achieve the desired appearance and the reduced
density, the proportion of cycloolefin copolymers (COCs) in the
base layer must be greater than 0.5% by weight, based on the weight
of the base layer. If, on the other hand, the cycloolefin copolymer
(COC) content is greater than 30%, the film cannot be disposed of
in an environmentally friendly manner.
[0007] It is furthermore necessary for the glass transition
temperature of the cycloolefin copolymer (COC) employed to be above
70.degree. C. It has been found that the desired effects with
respect to the density reduction of the film and with respect to
the appearance of the film are not achieved with a COC having a
glass transition temperature of below 70.degree. C. On the other
hand, if the glass transition temperature is below 70.degree. C.,
the raw material mixture has poor processing properties (poor
extrusion properties), the desired whiteness is no longer achieved,
and the regrind employed results in a film which has an increased
tendency towards yellowing. If, on the other hand, the glass
transition temperature of the cycloolefin copolymer (COC) selected
is above 270.degree. C., the raw material mixture can no longer be
homogeneously dispersed to an adequate extent in the extruder. This
results in a film having inhomogeneous properties.
[0008] In a preferred embodiment of the film according to the
invention, the glass transition temperature of the COCs used is in
the range from 90 to 250.degree. C. and in a particularly preferred
embodiment in the range from 110 to 220.degree. C.
[0009] Surprisingly, it has been found that the addition of a
cycloolefin copolymer (COC) in a PHC polymer matrix allows the
production of an opaque, glossy film having reduced density.
[0010] The film according to the invention has a single-layer or
multilayer structure. Single-layer embodiments are built up like
the COC-containing layer described below. Multilayer embodiments
have at least two layers and always include the COC-containing
layer and at least one further layer, where the COC-containing
layer can be the base layer, and, if desired, the interlayer or the
top layer of the multilayer film can also be the COC-containing
layer. In a preferred embodiment, the COC-containing layer forms
the base layer of the film having at least one top layer,
preferably having top layers on both sides, it being possible, if
desired, for an interlayer(s) to be present on one or both
sides.
[0011] In a further preferred embodiment, the COC-containing layer
forms an interlayer of the multilayer film. Further embodiments
with COC-containing interlayers have a five-layer structure and, in
addition to an optionally COC-containing base layer, have
COC-containing interlayers on both sides. In a further embodiment,
the COC-containing layer can form a top layer on the base layer or
interlayer. If desired, both top layers can be COC-containing. For
the purposes of the present invention, the base layer is the layer
which makes up more than from 30% to 100%, preferably from 50 to
90%, of the total film thickness and has the greatest layer
thickness. The top layers are the layers which form the outer
layers of the film. Interlayers are of course provided between the
base layer and the top layers.
[0012] The COC-containing layer, which is, if desired, the single
layer of the film according to the invention, comprises a polymer I
made from at least one hydroxycarboxylic acid, at least one COC and
optionally, further additives in effective amounts in each case. In
general, this layer comprises at least from 50 to 99.5% by weight,
preferably from 60 to 98% by weight, in particular from 70 to 98%
by weight, of a polymer I made from at least one hydroxycarboxylic
acid, based on the weight of the layer.
[0013] The base layer of the film comprises at least one polymer I
made from at least one hydroxycarboxylic acid, referred to as PHC
(polyhydroxycarboxylic acids) below, in general in an amount of
from 50 to 99.5% by weight, preferably from 70 to 95% by weight.
These are taken to mean homopolymers or copolymers built up from
polymerized units of preferably aliphatic hydroxycarboxylic acids.
Of the PHCs which are suitable for the present invention,
polylactic acids are particularly suitable. These are referred to
as PLA (polylactide acid) below. Here too, the term is taken to
mean both homopolymers built up only from lactic acid units and
copolymers comprising predominantly lactic acid units (>50%) in
combination with other aliphatic hydroxylactic acid units.
[0014] Suitable monomers of aliphatic polyhydroxycarboxylic acid
(PHC) are, in particular, aliphatic mono-, di- or
trihydroxycarboxylic acids and dimeric cyclic esters thereof, of
which lactic acid in its D or L form is preferred. A suitable PLA
is, for example, polylactic acid from Cargill Dow (Nature-Works).
The preparation of polylactic acid is known from the prior art and
is carried out via catalytic ring-opening polymerization of lactide
(1,4-dioxane-3,6-dimethyl-2,5-dione), the dimeric cyclic ester of
lactic acid, for which reason PLA is also frequently known as
polylactide. The preparation of PLA has been described in the
following publications: U.S. Pat. No. 5,208,297, U.S. Pat. No.
5,247,058 or U.S. Pat. No. 5,357,035.
[0015] Preference is given to polylactic acids built up exclusively
from lactic acid units. Of these, particular preference is given to
PLA homopolymers comprising 80-100% by weight of L-lactic acid
units, corresponding to from 0 to 20% by weight of D-lactic acid
units. In order to reduce the crystallinity, even higher
concentrations of D-lactic acid units may also be present as
comonomer. If desired, the polylactic acid may additionally
comprise aliphatic hydroxycarboxylic acid units other than lactic
acid as comonomer, for example glycolic acid units,
3-hydroxypropanoic acid units, 2,2-dimethyl-3-hydroxypropanoic acid
units or higher homologues of the hydroxycarboxylic acids having up
to 5 carbon atoms.
[0016] Preference is given to lactic acid polymers (PLAS) having a
melting point of from 110 to 170.degree. C., preferably from 125 to
165.degree. C., and a melt flow index (measurement DIN 53 735 at a
load of 2.16 N and 190.degree. C.) of from 1 to 50 g/10 min,
preferably from 1 to 30 g/10 min. The molecular weight of the PLA
is in the range of from at least 10,000 to 500,000 (number
average), preferably from 50,000 to 300,000 (number average). The
glass transition temperature Tg is in the range from 40 to
100.degree. C., preferably from 40 to 80.degree. C.
[0017] In accordance with the invention, the COC-containing layer
or the Film in the case of single-layer embodiments comprises a
cycloolefin copolymer (COC) in an amount of at least 0.5% by
weight, preferably from 1 to 30% by weight and particularly
preferably from 2 to 10% by weight, based on the weight of the
layer or based on the weight of the film in the case of
single-layer embodiments.
[0018] Cycloolefin polymers are homopolymers or copolymers built up
from polymerized cycloolefin units and, if desired, acyclic olefins
as comonomer. For the present invention, suitable cycloolefin
polymers are those which comprise from 0.1 to 100% by weight,
preferably from 10 to 99% by weight, particularly preferably 50-95%
by weight, in each case based on the total weight of the
cycloolefin polymer, of polymerized cycloolefin units. Particularly
suitable cycloolefin polymers are described in detail in EP 1 068
949, which is expressly incorporated herein by way of
reference.
[0019] Of the cycloolefin copolymers described above and described
in EP 1 068 949, particular preference is given to those which
comprise polymerized units of polycyclic olefins having a
norbornene basic structure, particularly preferably norbornene or
tetracyclododecene. Particular preference is also given to
cycloolefin copolymers (COCs) which comprise polymerized units of
acyclic olefins, in particular ethylene. Particular preference is
in turn given to norbornenelethylene and
tetracyclododecenelethylene copolymers which comprise from 5 to 80%
by weight, preferably from 10 to 60% by weight, of ethylene (based
on the weight of the copolymer).
[0020] The cycloolefin polymers described generically above and in
EP 1 068 949 generally have glass transition temperatures of
between 100.degree. C. and 400.degree. C. For the invention, use
can be made of cycloolefin copolymers (COCs) which have a glass
transition temperature of above 70.degree. C., preferably above
90.degree. C. and in particular above 110.degree. C. The viscosity
number (decalin, 135 DEG C, DIN 53 728) is advantageously between
0.1 and 200 ml1 g, preferably between 50 and 150 ml/g.
[0021] The preparation of the cycloolefin copolymers (COCs) is
carried out by heterogeneous or homogeneous catalysis using
organometallic compounds and is described in a multiplicity of
documents. Suitable catalyst systems based on mixed catalysts
comprising titanium or vanadium compounds in combination with
organoaluminium compounds are described in DD 109 224, DD 237070
and EP-A-0 156 464. EP-A-0 283 164, EP-A-0 407 870, EP-A-0 485 893
and EP-A-0 503 422 describe the preparation of cycloolefin
copolymers (COCs) using catalysts based on soluble metal-locene
complexes. The cycloolefin polymer preparation processes described
in the above-mentioned documents are expressly incorporated herein
by way of reference.
[0022] The cycloolefin copolymers are incorporated into the film
either in the form of pure granules or as granulated concentrate
(masterbatch) by pre-mixing the granules of PHC, preferably PLA,
with the cycloolefin copolymer (COC) or the cycloolefin copolymer
(COC) masterbatch and subsequently feeding the mixture to the
extruder. In the extruder, the components are mixed further and
warmed to the processing temperature. It is advantageous for the
process according to the invention for the extrusion temperature to
be above the glass transition temperature Tg of the cycloolefin
copolymer (COC), in general at least 10.degree. C., preferably from
15 to 100.degree. C., in particular from 20 to 150.degree. C.,
above the glass transition temperature of the cycloolefin copolymer
(COC).
[0023] Besides the COC-containing layer, the film preferably
additionally has further layers, which can form the base layer, an
interlayer or a top layer. These further layers are built up from
the polyhydroxycarboxylic acid (PHC) described above for the
COC-containing layer. For these further layers, PLAs are preferred
in the same way.
[0024] The COC-containing layer and the other layers may
additionally comprise conventional additives, such as neutralizers,
stabilizers, antiblocking agents, lubricants and other fillers.
They are advantageously added to the polymer or the polymer mixture
even before melting. As stabilizers, use is made, for example, of
phosphorus compounds, such as phosphoric acid or phosphoric acid
esters.
[0025] Typical antiblocking agents are inorganic and/or organic
particles, for example calcium carbonate, amorphous silicic acid,
talc, magnesium carbonate, barium carbonate, calcium sulphate,
barium sulphate, lithium phosphate, calcium phosphate, magnesium
phosphate, aluminium oxide, carbon black, titanium dioxide, kaolin
or crosslinked polymer particles, for example polystyrene or
acrylate particles.
[0026] As additives, it is also possible to select mixtures of two
or more different antiblocking agents or mixtures of antiblocking
agents of the same composition, but different particle size. The
particles can be added to the polymers of the individual layers of
the film in the advantageous concentrations in each case, directly
or via masterbatches during extrusion. Antiblocking agent
concentrations of from 0 to 10% by weight (based on the weight of
the respective layer) have proven particularly suitable. A detailed
description of the antiblocking agents is given, for example, in
EP-A-0 602 964.
[0027] In order to improve the whiteness of the film, the
COC-containing layer or at least one of the further layers may
comprise a pigment. It has proven particularly favourable here to
select barium sulphate in a mean particle size of 0.3-0.8 .mu.m,
preferably 0.4-0.7 .mu.m, or titanium dioxide having a mean
particle size of 0.05-1 .mu.m, as additional additives. The film is
thereby given a bright, white appearance. In general, the
COC-containing layer and/or a further layer in these embodiments
comprises from 1 to 25% by weight, preferably from greater than 1
to 20% by weight and in particular from 1 to 15% by weight of
pigments, in each case based on the weight of the layer.
[0028] The total thickness of the film can vary within broad limits
and depends on the intended application. The preferred embodiments
of the film according to the invention have total thicknesses of
from 4 to 200 .mu.m, preferably from 8 to 150 .mu.m, particularly
preferably from 10 to 100 .mu.m. The thickness of any interlayer(s)
present is generally in each case, independently of one another,
from 0.5 to 15 .mu.m, where interlayer thicknesses of from 1 to 10
.mu.m, in particular from 1 to 8 .mu.m, are preferred. The stated
values are in each case based on one interlayer. The thickness of
the top layer(s) is selected independently of the other layers and
is preferably in the range from 0.1 to 5 .mu.m, in particular from
0.2 to 3 .mu.m, where top layers applied to both sides may be
identical or different with respect to thickness and composition.
The thickness of the base layer arises correspondingly from the
difference between the total thickness of the film and the
thickness of the top layer(s) and interlayer(s) applied and can
therefore vary within broad limits analogously to the total
thickness.
[0029] The various embodiments of the film according to the
invention described above can be used as substrate for subsequent
metallation. In this case, embodiments, in particular, which are
metallized on the surface of a COC-containing layer, i.e.
single-layer embodiments and those having a corresponding
COC-containing layer as top layer, have proven particularly
advantageous. It has been found that layers of COC and polymer made
from at least one hydroxycarboxylic acid have particularly good
metal adhesion.
[0030] Furthermore, the opaque film described can be employed as
label film and as packaging film for the packaging of foods and
articles of use. Owing to advantageous twist-wrap properties, which
are known per se of PLA film and are not impaired by the addition
of the vacuole-forming COC, the film is also very highly suitable
for twist-wrap packaging for sweets, tampons and the like.
[0031] The invention furthermore relates to a process for the
production of the film according to the invention by the extrusion
or coextrusion process, which is known per se. In this process, the
melt(s) corresponding to the single-layer film or the layers of the
film is (are) extruded/coextruded through a flat-film die, the
resultant film is taken off over one or more roll(s) for
solidification, the film is subsequently biaxially stretched
(oriented), and the biaxially stretched film is heat-set and, if
desired, corona- or flame-treated on the surface layer intended for
the treatment.
[0032] The biaxial stretching is generally carried out
sequentially. This stretching is preferably carried out firstly in
the longitudinal direction (i.e. in the machine direction,=MD
direction) and subsequently in the transverse direction (i.e.
perpendicular to the machine direction,=TD direction). This results
in orientation of the molecule chains. The stretching in the
longitudinal direction is preferably carried out with the aid of
two rolls running at different speeds corresponding to the target
stretching ratio. The transverse stretching is generally carried
out using a corresponding tenter frame. The further description of
the film production uses the example of flat-film extrusion with
subsequent sequential stretching.
[0033] The melt(s) are forced through a flat-film die (slot die),
and the extruded film is taken off over one or more take-off rolls
at a temperature of from 10 to 100.degree. C., preferably from 30
to 80.degree. C., during which it cools and solidifies.
[0034] The resultant film is then stretched longitudinally and
transversely to the extrusion direction. The longitudinal
stretching is preferably carried out at a temperature of from 40 to
120.degree. C., preferably from 50 to 80.degree. C., advantageously
with the aid of two rolls running at different speeds corresponding
to the target stretching ratio, and the transverse stretching is
preferably carried out at a temperature of from 50 to 150.degree.
C., preferably from 70 to 100.degree. C., with the aid of a
corresponding tenter frame. The longitudinal stretching ratios are
in the range from 1.5 to 8, preferably from 2 to 5.5. The
transverse stretching ratios are in the range from 3 to 10,
preferably from 4 to 7.
[0035] The stretching of the film is followed by heat-setting (heat
treatment) thereof, during which the film is held at a temperature
of from 60 to 150.degree. C. for from about 0.1 to 10 seconds. The
film is subsequently wound up in a conventional manner using a
wind-up device.
[0036] If desired, the film can be coated in order to adjust
further properties. Typical coatings are adhesion-promoting,
antistatic, slip-improving or dehesive coatings. These additional
layers can, if desired, be applied by in-line coating by means of
aqueous dispersions before the transverse stretching or
off-line.
[0037] The film according to the invention is distinguished by good
whiteness and by good opacity. It is highly suitable for the
packaging of light- and/or air-sensitive foods and semi-luxury
products. In addition, it is also suitable for use in the
industrial sector, for example in the production of embossing films
or as label film. It has been found that the addition of COC
produces vacuole-like cavities in the film, which reduce the
density of the film compared with the corresponding density of the
raw materials. In accordance with the invention, the density is in
the range from 0.6 to 1 g/cm.sup.3.
[0038] It has additionally been found that the addition of COC
improves the stretchability of the film. Compared with pure PLA
films containing no further additives, it has been possible
considerably to increase the longitudinal and transverse stretching
factors.
[0039] The following measurement values were used to characterize
the raw materials and films:
[0040] Whiteness and Opacity
[0041] The whiteness and opacity are determined with the aid of the
"ELREPHO" electric remission photometer from Zeiss, Oberkochem
(DE), standard illuminant C, 2 DEG standard observer. The opacity
is determined in accordance with DIN 53 146. The whiteness is
defined as WG=RY+3RZ-3RX. WG=whiteness, Rx, Ry, Rz=corresponding
reflection factors on use of the Y, Z and X colour measurement
filter. The white standard used is a pressed disc of barium
sulphate (DIN 5033, Part 9). A detailed description is described,
for example, in Hansl Loos "Farbmessung" [Colour Measurement],
Verlag Beruf und Schule, Itzehoe (1989).
[0042] Light Transmission
[0043] The light transmission is measured in accordance with ASTM-D
1033-77.
[0044] Glass Transition Temperature
[0045] The glass transition temperature Tg was determined with
reference to film samples with the aid of DSC (differential
scanning calorimetry) (DIN 73 765). A DSC 1090 from DuPont was
used. The heating rate was 20 K/min, and the sample weight was
about 12 mg. In the first heating operation, the glass transition
Tg was determined. The samples frequently exhibited enthalpy
relaxation (a peak) at the beginning of the step-shaped glass
transition. The Tg was taken to be the temperature at which the
step shaped change in the heat capacity--independently of the
peak-shaped enthalpy relaxation--reached half its height in the
first heating operation. In all cases, only a single glass
transition step was observed in the thermogram during the first
heating.
[0046] The invention is explained below with reference to working
examples.
EXAMPLE 1
[0047] An opaque single-layer PLA film having a thickness of 30
.mu.m was produced by extrusion and subsequent stepwise orientation
in the longitudinal and transverse directions. This layer was built
up from about 95% by weight of a polylactic acid having a melting
point of 135.degree. C. and a melt flow index of about 3 g/10 min
and a glass transition temperature of 60.degree. C. and about 5% by
weight of COC (Ticona Topas 6013) having a Tg of 140.degree. C. The
layer additionally comprised stabilizers and neutralizers in
conventional amounts. The production conditions in the individual
process steps were as follows:
1 Extrusion: Temperatures 170-200.degree. C. Temperature of the
take-off roll: 60.degree. C. Longitudinal stretching: Temperature:
68.degree. C. Longitudinal stretching ratio: 4.0 Transverse
stretching: Temperature: 88.degree. C. Transverse stretching ratio
5.5 (effective): Setting: Temperature: 75.degree. C. Convergence:
5%
[0048] In this way, an opaque film having characteristic
mother-of-pearl-like gloss and a reduced density of about 0.75
g/cm.sup.3 was obtained.
EXAMPLE 2
[0049] A single-layer film was produced as described in Example 1.
The COC content here was reduced to about 3% by weight and the PLA
content was increased correspondingly. Under the process
conditions, the longitudinal stretching factor was reduced to 3.5.
In this way, an opaque film having characteristic
mother-of-pearl-like gloss and a reduced density of about 0.8
g/cm.sup.3 was likewise obtained.
EXAMPLE 3
[0050] A film was produced as described in Example 1. In contrast
to Example 1, top layers of PLA were applied to both sides of the
COC-containing layer. The top layers were built up from a
polylactic acid having a melt flow index of about 2.6 g/10 min. The
process conditions from Example 1 were not changed. In this way, a
symmetrical three-layer opaque PLA film was obtained, the density
of this film was 0.77 glcm.sup.3.
COMPARATIVE EXAMPLE 1
[0051] A film was produced as described in Example 1. In contrast
to Example 1, the film comprised no COC and consisted of about 100%
by weight of PLA. The process conditions had to be changed. The
longitudinal stretching could only be carried out at a longitudinal
stretching factor of 2.5. Higher longitudinal stretching factors
resulted in tears.
COMPARATIVE EXAMPLE 2
[0052] A film was produced as described in Example 1. In contrast
to Example 1, 5% by weight of a CaCO.sub.3 having a mean particle
size of 3 .mu.m was employed instead of the COC. It was only
possible to stretch this composition in the longitudinal direction
by a maximum factor of 2.5. Here too, tears occurred at higher
longitudinal stretching factors. This film did not exhibit an
opaque appearance. Only a certain milky haze was achieved. The
density of the film was 1.25 glcm.sup.3 and was thus not
reduced.
* * * * *